1. Field of the Invention
The present invention relates generally to a method and apparatus for intermittent recording in a time-lapse video tape recorder, and in particular, to a control method for intermittent recording in a time-lapse video tape recorder that is capable of calculating a recording pause period based on a time-lapse recording mode, and capable of (1) stopping the rotation of the head drum temporarily and/or (2) unloading the magnetic tape that has been loaded for recording when the calculated recording pause period is longer than a predetermined period of time.
2. Brief Description of the Prior Art
Unlike ordinary continuous video tape recorders, which record every frame of video signals, the time-lapse video tape recorder intermittently records video signals from several video cameras or the like on a magnetic tape at a pre-selected regular interval while the recorder repeatedly runs and stops. Time-lapse video tape recorders have been used in various areas requiring long-time recording, such as security monitoring systems in banks and museums. As shown in FIG. 8, a time-lapse video tape recorder comprises switching unit 10, which selects a signal among video signals received from several video cameras; control unit 20, which extracts one frame intermittently from the continuous video signal received from the switching unit 10; and recording unit 30 which records the video signal as a frame is received from the control unit 20 on a frame basis in each video track of a magnetic tape.
The recording unit 30 comprises a signal processing unit, which processes the video signal for recording, and mechanical elements. The mechanical elements include a loading motor which moves a loading post into a loading/unloading state of the magnetic tape; a drum motor which rotates a head drum on which video heads are mounted to record/reproduce the video signal on/from the magnetic tape; and a capstan motor which rotates a capstan shaft to drive the magnetic tape at a predetermined tape running speed.
For example, in a conventional time-lapse video tape recorder configured as above, if a magnetic tape of 2 hours running time is used for recording during 48 hours, then the switching unit 10 switches to the next video camera at intervals of time corresponding to 24 video frames (48 hours/2 hours=24). The switching unit 10 receives a video signal from the video camera selected, and sends the received video signal to the control unit 20. Then, the control unit 20 extracts one frame out of the video signal received from the switching unit 10 and records the extracted frame on the magnetic tape while moving a single video track of the magnetic tape by driving the capstan motor in the recording unit 30.
In case of the prior art above, while the video signal is recorded on the magnetic tape intermittently, the magnetic tape is loaded in the recording unit 30 even when no video signal is recorded. The rotation of the capstan motor is stopped temporarily when recording is paused, but the head drum always rotates. Therefore, high-precision control of the capstan motor is required to perform repeated run-and-stop of the magnetic tape by one video track. In addition, because the magnetic tape is always in contact with the head drum, even when no video signal is recorded on the magnetic tape, friction between the magnetic tape and the head drum lowers the quality of the video signal recorded on the magnetic tape and shortens the life of the magnetic tape and head drum.
One objective of the present invention is to solve the above mentioned problems in the conventional method, and a further objective is to provide a control method and apparatus for intermittent recording in time-lapse video tape recorder that is capable of unloading the magnetic tape or temporarily stopping the rotation of the head drum when recording is stopped.
Another objective of this invention is to provide a control method and apparatus for intermittent recording in a time-lapse video tape recorder that selectively performs unloading of the magnetic tape or temporary stopping of the rotation of the head drum depending on whether or not a recording pause period is longer than a predetermined period of time.
The present invention is characterized as a method for the intermittent recording in the time-lapse video tape recorder, which comprises the steps of: confirming whether the recording is stopped temporarily in the intermittent recording mode; and either unloading the magnetic tape or temporarily stopping the rotation of the head drum during the recording pause period.
According to the present invention, in the control method of the head drum or tape unloading of the time-lapse video tape recorder, a frame extraction ratio of a video signal, or a ratio of the number of fields to be skipped and the number of field to be recorded, is calculated from a recording time in a time-lapse recording mode that is set by a user. Based on a frame extraction ratio and the size of a memory in which the selected input video frames are temporarily stored before recording, a recording pause period or the time during which no video signal is recorded is calculated.
If the recording pause period is longer than a predetermined reference period of time, the magnetic tape is unloaded or the rotation of the head drum is stopped temporarily during the recording pause period. If the recording pause period is not longer than a predetermined reference period of time, the head drum keeps rotating and contacting with the magnetic tape during the recording pause period as in conventional time-lapse video tape recorders.
In the case where a recording pause period is long, the intermittent recording method of the present invention can prolong the life of the head drum and the magnetic tape through reduction of friction between the magnetic tape and the head drum and reduce the power consumption by the rotation of the head drum.